Pesticide drift in aerial pesticide application process is one of the important factors of pesticide pollution. Pesticide drift is physical movement of pesticide droplets or particles migrating from target area to non-target area in the sky under uncontrolled condition, during or after the aerial spraying process. Pesticide drift includes evaporation drift caused by volatilization of pesticide active ingredients, and windy drift, which mainly refers to the disappearance or re-settlement process of small droplets in the fog carried out of the target area by air flow. Droplets drift occurs invariably in the aerial spraying process; and pesticide drift occurs in all the spraying processes to a certain extent. Part of the pesticide fog in the aerial spraying may drift even a few kilometers away influenced by wind speed, tip vortex of the aircraft, flight altitude, flight speed and the like. The drift has serious effects on the pesticide application result and the environment: (1) the quantity of sprayed pesticide may be non-uniform when spraying by the uniform patrol spray manner, wherein some areas are applied with no pesticide but some other areas are applied with excessive pesticide, which causes the waste in pesticide and incompleteness in the result of pesticide application to some degree; (2) most of the pesticides are toxic or may generate toxic substances and greenhouse gasses after degradation. When the invisible gasification pesticide fog clouds drift out of the spray area, water, healthy vegetation, and forest may be polluted, greenhouse gasses can be generated, which may result in an immeasurable impact on the environment; and (3) pesticide fog may drift to residential areas unconsciously which could harm the health of residents. It may cause acute or chronic poisoning when a great quantity of pesticides gets into the human body through mouth, respiratory tract or skin.
In the current pesticide application operation, the fog droplets are sampled commonly by laying oil sensitive paper and water-sensitive paper on the ground (Visual and Image System Measurement of Spray Deposits Using Water-sensitive Paper, Applied Engineering in Agriculture. 2003, 19 (5): 549-552), and the spraying result is obtained based on pesticide fog coverage, droplet size, and other information calculated by image processing algorithms.
For the detection of the pesticide residing in the air, adsorptive process is usually used, i.e., extracting the air to be measured with a large flow gas sampler and feeding the extracted air through glass fiber filter film or adsorbent column constituted by adsorbent, then eluting the air with an organic solvent and concentrating the solvent to measure with an instrument. For example, Li Chengquan et al. have studied distribution of pesticide fog concentration and drift state by depositing a plurality of air samplers in different positions in a greenhouse with the method above (Research on the Distribution and Visualization of Pesticide Fog Concentration Field in Confined Spaces, Jiangsu University, a master's degree thesis, 2009).
Information like pesticide fog coverage and fog droplet size may be obtained by the method of laying oil-sensitive papers and water-sensitive papers on the ground, but the method has the following shortcomings:
(1) only the spray level of certain areas on the ground can be obtained, which cannot fully reflect the drift state of pesticide fog in the air;
(2) poor in effectiveness;
(3) the concentration and composition of the fog cannot be obtained; and
(4) tiny droplets which suspend in the air all the time cannot be detected.
The pesticide in the air can be monitored with the gas sampling method, but the method has the following defects:
(1) only the collected gas is analyzed, which cannot reflect fully the distribution of the pesticide fog;
(2) the monitoring cannot be performed in real time and continuously;
(3) sampling and pre-treatment processes are complex, time-consuming, and laborious; and
(4) the sampling and the analyzing for upper air pesticide fog are hard to be performed.